1. Field of the Invention
The present invention relates to an image processing technique for improving line visibility.
2. Description of the Related Art
An image forming engine (also referred to as a printing engine) in an image forming apparatus fixes a coloring agent to a sheet such as paper, to print an image on the paper. The printing engine makes an amount of the coloring agent per pixel variable, to represent gradation of the image. A user may desire to improve line visibility in such a manner that a line to be printed looks thick and wide in the image forming apparatus.
Japanese Patent Application Laid-Open No. 2007-300206 discusses processing for increasing the density of pixels composing a line included in image data to thicken the line to be printed. Through this processing, in the image forming apparatus, an amount of a coloring agent per pixel increases. Generally, when the amount of the coloring agent per pixel increases, the area of the coloring agent per pixel also increases. Thus, the density and the width of the line per unit area also increase. For a user, the line seems to have become thicker and wider. That is, line visibility is improved.
However, in some cases, only by the processing discussed in Japanese Patent Application Laid-Open No. 2007-300206, line visibility may not be improved. For example, the density of the pixels constituting the line may be sufficiently high (close to the maximum density). In this case, the density of the pixels cannot be increased beyond the maximum density when increasing the density of the line. Therefore, line visibility has been difficult to improve through the processing for increasing the density of the line having a sufficiently high density.